The present invention relates to a variable displacement compressor, and more particularly, to an improvement of lubrication performance.
When a compressor operates with insufficient refrigerant, the temperature of the refrigerant might become abnormally high. In this case, the lubricant contained in the refrigerant is reduced. In the variable displacement compressors disclosed in Japanese Laid-Open Patent Publication No. 62-91672 and Japanese Laid-Open Patent Publication No. 3-100381, the amount of lubricant contained in refrigerant sent from the discharge pressure zone to the control pressure chamber is small, the amount of lubricant sent to the control pressure chamber is insufficient. If the compressor operates at a large displacement, that is, with a great inclination angle of the swash plate, when there is insufficient lubricant, seizing may occur between the swash plate and the shoes.
The variable displacement compressor disclosed in Japanese Laid-Open Patent Publication No. 62-91672 has a pressure controlling section that incorporates a shape changing member between a discharge chamber and a signal pressure chamber (control pressure chamber). The shape changing member includes a spring made of a shape memory alloy that responds to temperature. When the temperature of refrigerant is equal to or higher than a predetermined temperature, the urging force of the spring is rapidly increased so that a high pressure valve of the pressure controlling section is opened. When the high pressure valve is open, the amount of refrigerant sent from the discharge chamber to the signal pressure chamber increases. Accordingly, the pressure in the signal pressure chamber increases, and the inclination angle of the wobble plate is reduced. As a result, the seizing between the swash plate and the shoes is avoided.
In the variable displacement compressor disclosed in Japanese Laid-Open Patent Publication No. 62-91672, when the temperature of refrigerant is equal to or higher than a predetermined temperature, the amount of refrigerant sent to the signal pressure chamber is increased, so that the inclination angle of the wobble plate is reduced. On the other hand, in the compressor disclosed in Japanese Laid-Open Patent Publication No. 62-91672, the refrigerant in the signal pressure chamber flows out to the suction chamber through a release passage. As a result, in order to maintain a small inclination angle of the wobble plate, refrigerant needs to be constantly supplied to the signal pressure chamber at a great flow rate. However, since the temperature of the refrigerant is high, constantly supplying the refrigerant to the signal pressure chamber can have an adverse influence on the reliability of sliding members.
Also, since the refrigerant in the signal pressure chamber flows out to the suction chamber, lubricant flows out of the signal pressure chamber together with the refrigerant. In addition, in a state where the temperature of the refrigerant is abnormally high, the amount of lubricant in the refrigerant has been reduced, and therefore only a small amount of lubricant is sent to the signal pressure chamber. The amount of lubricant in the signal pressure chamber will therefore be insufficient.